Worker exposure to s,s,s-tributylphosphorotrithioate (78488) (DEF) and general work conditions were investigated at the Belridge Farms (SIC-0722) in Bakersville, California, on November 15 and 17, 1978. Thirty-three personal air and 11 dermal samples were collected and analyzed using gas chromatographic methods. Minor and major injuries were treated by a local physician or hospital, respectively. Cholinesterase determinations were made every week. No preemployment examinations were given. Air DEF concentrations ranged from 6.9 to 83.4 nanograms per cubic meter, and dermal samples ranged from 0.05 to 1.70 milligrams per 8 hours. The author recommends additional sampling during typical weather conditions.